Two years ago I came up with an idea to recycle cubies (20 litre HDPE oil containers). I filled about 30 of them with water, arranged them in a rectangle and covered it with black plastic sheet. I then filled the middle of the rectangle with with soil and planted tomatoes in the Raised Water Beds. I did this in my polytunnel and got spectacular results. In spring time I measured the soil temp at 6 degrees C outside in the garden, 10 degrees C in the polytunnel and 14 degrees C in the raised beds. Also because of the heat storage capacity the beds the nightime cooling was almost neglible. The tomatoes started earlier and cropped heavier than ever before.Last year I decided to construct a raised water bed outside in the yard and it worked very well but when winter came I ran into trouble. The water froze and burst many of the cubies. By spring time it had to be completely rebuilt. I realized then that I had a ready supply of a liquid which is a perfect antifreeze, glycerine. I did some tests and found that 50% glycerine / 50% water will not freeze in my freezer which is -23 degrees C. A single raised bed 3 metres long recycles 30 plastic containers and 300 litres of glycerine.This will work with KOH or NaOH glygerine.I have attached a picture of a raised bed under construction. There are more on my imageshack.

Great idea!Whats the viscosity of the 50/50 glycerin water mix like?I picked up a free deep freeze this winter and intend to make a glycerin antifreeze solution to fill it and then pump through my condenser.Jon

My glycerine is KOH based so its very liquid. When mixed with water 50/50% its about the same viscosity as biodiesel. I should mention that I distill the methanol out of my glycerine before using it for my raised beds.A friend of mine has just bought a house with underfloor heating powered by an oil furnace. He's finding it very expensive to heat. I have built a biodiesel processor for him so that he can use biodiesel instead of kerosene.I have been thinking about an idea which might help him. its just an idea at the moment but Im going to float it and see what all of you think.His heating system requires a supply of warm rather than hot water. 40 degrees C is considered hot enough for this system. My idea is to build a solar wall which on sunny winter days might supply him with warm water. The layout is roughly this, a line of 50 steel oildrums on an insulated base, each one connected to the next. An insulated wooden wall behind the drums, an insulated tar paper roof above and a clear corrugated PVC panels to the front. The drums would be filled with glycerine and would heat up throughout the day. At night a pump and heat exchanger would extract the heat from the solar wall and supply the underfloor heating in the house. I did a little experiment with 2 oildrums of glycerine. I improvised a shelter over them and put some corrugated pvc in front. It was very leaky but on a bright winters day the temp of the glycerine rose fron 9 degrees C to 21 degrees C. can any one tell me is this enough, bearing in mind that there would be 10,000 litres of glycerine in the proposed solar wall?

Thanks Legal Eagle, those solar heating boxes are very similar to what I was thinking of. Before putting a lot of effort and money into the project I want to try to calculate how much heat would be needed and how much my setup might produce.